The present invention relates to a circuit for removing unwanted glitches from signals and more particularly, to a glitch removal circuit that removes both positive and negative glitches from signals.
Electrical circuits often have to operate in noisy environments. Noise may be introduced into signals from a number of different sources such as cross talk between signal lines, transients caused by logic gates, electromagnetic interactions between various circuits, etc. Such noise generates spurious components in the input or output signals of the circuit. These spurious components are referred to as glitches.
Glitches distort the size and shape of the signal pulse. A glitch may cause a high signal to become low or a low signal to become high. A positive glitch may occur on a logic low signal causing it to overshoot for a brief period. Similarly, a negative glitch may occur on a logic high signal causing it to undershoot for a brief period.
Glitches, if untreated, may affect the operation of a circuit and hamper the performance of the entire system of which the circuit is a part. In digital systems, glitches may tamper with clock signals and handshake signals that drive various circuits within the system. For example, in a memory array if a glitch occurs in an address signal while it is being latched, then the wrong address may be read, which may lead to an unrecoverable system error. Also, glitches may cause chips to receive or transmit noisy signals to other chips. Thus, circuits must be designed to anticipate and handle spurious pulses or glitches in order to maintain the consistency and reliability of electrical circuit operation. A glitch removal circuit tries to remove glitches and restore an input signal to its original shape.
Existing glitch removal circuits suffer from a number of drawbacks, such as being overly complex, requiring a large number of components, and requiring a large amount of space. Hence, these circuits are difficult to implement, use valuable chip real estate, and draw excess current. Further, such circuits may also introduce an excessively long delay in the output signal as compared with the duration of the glitch to be filtered, leading to slow signal processing speeds. This may also affect the synchronization of output signals with other circuits. A glitch removal circuit should also be able to remove both positive and negative glitches simultaneously, and pulses of short duration, yet without distorting the input signal pulse width.
Accordingly, there is a need for a glitch removal circuit that can remove both positive and negative glitches, has a low delay time, and a small circuit area. Further, the circuit should be able to remove very short duration glitches.